1. Field of the Invention
The present disclosure relates to a ceramic substrate for mounting a component such as a light-emitting diode and a method of manufacturing the ceramic substrate.
2. Description of Related Art
Light-emitting diodes (LEDs) are well known light-emitting elements. In recent years, a high-brightness blue LED has been put into practical use. The blue LED can be therefore combined with red and green LEDs to obtain high-brightness white light, facilitating the development of a light bulb or an automobile headlight using these three color LEDs. In general, LEDs have the advantage of smaller electric power consumption. Thus, the use of LEDs in headlights can reduce battery load. LEDs also have the advantage of long operating life, thereby being expected to be applied in lighting fixtures, such as fluorescent lamps and light bulbs. For using LEDs in the above applications, high performance of a LED package is an important factor in maximizing the advantages of the LEDs. In this respect, a ceramic package may be suitable for mounting LEDs because of its superior properties such as durability, heat resistance, corrosion resistance, and heat dissipation, compared with, for example, an organic package.
The ceramic package includes a ceramic substrate having an insulator part and a conductor part. The insulator part is made of, for example, an alumina-based ceramic material. The conductor part is made of a metal (such as tungsten or molybdenum) that can be co-fired with alumina. Further, a principal surface of the ceramic substrate has a connecting terminal portion for connection with the LED. The connecting terminal portion includes a copper layer made of copper and a metal layer (such as a nickel layer or a gold layer) covering the copper layer, which are successively stacked by any technique well known in the art (such as a sputtering or plating technique). The copper layer of the connecting terminal portion has poor adhesion property to the ceramic layer. Thus, a contact layer of titanium is formed as an under layer for the copper layer to improve the adhesion property of the connecting terminal portion (see, for example, JP-A-2010-223849).